Unexpected SiC nanowires growth during spark plasma sintering of WC-10Si: A comparative study on phase formation and microstructure properties against WC-10Co cermet

Abstract

In the present work, SiC nanowires were formed unexpectedly during spark plasma sintering of WC-10 wt%Si cermet. The microstructure, hardness, bending strength and fracture toughness of WC-10 wt%Si were compared with conventional WC-10 wt%Co. The sintering temperatures were chosen according to time-temperature-displacement curves to enhance maximum shrinkage of composites containing Si and Co at temperatures of 1850° and 1350 °C, respectively. Thermodynamic investigations showed negative Gibbs free energy of the formation of WSi2 and SiC compounds during sintering process while the positive amounts of ΔG were calculated for the possible formation of intermetallic compounds in WC-10 wt%Co composite. XRD investigations approved the formation of WSi2 and SiC compounds while the reaction between WC and Co led to the formation of η phase as expected. The microstructure observations revealed nanowire shapes of SiC particles distributed uniformly. The bending strength of 583 ± 31 MPa and fracture toughness of 6.2 MPa m1/2 were measured for WC-10 wt%Si composite, these amounts were lower compared to bending strength and fracture toughness of WC-10 wt%Co composite (1032 ± 26 MPa and 16.4 MPa m1/2, respectively). Besides, the hardness of 2147 ± 31 and 1622 ± 28 Vickers was obtained for WC-10 wt%Si and WC-10 wt%Co composites, respectively. The weak mechanical properties of WC-10 wt%Si composite were related to the presence of pores between SiC nanowires which acted as crack propagation centers.